Protein kinases constitute a large family of structurally related enzymes that are responsible for the control of a wide variety of signal transduction processes in the cell. They have been shown to be key regulators in most cellular functions including proliferation, cell metabolism, cell survival, apoptosis, DNA damage repair, cell motility, . . . The protein kinase activity is based on phosphorylation events which act as molecular on/off switches that can modulate or regulate the target protein's biological function. Phosphorylation of target proteins occurs in response to a variety of extracellular signals (hormones, neurotransmitters, growth and differentiation factors, etc.), cell cycle events, environmental or nutritional stresses etc. The appropriate protein kinase functions in signalling pathways to activate or inactivate, for example, a metabolic enzyme, regulatory protein, receptor, cytoskeletal protein, ion channel or pump, or transcription factor. Uncontrolled signalling due to defective control of protein phosphorylation has been implicated in a number of diseases, including, for example, inflammation, allergies, immune diseases, CNS disorders, angiogenesis. Furthermore, it is not surprising that they often become oncogenes, thereby having major implications in multiple cancers, due to their crucial functions in apoptosis, DNA damage repair, proliferation, . . . .
Amongst the families of protein kinases, one particular example is the receptor tyrosine kinase class III family including FLT3. FLT3 (FMS-like tyrosine kinase 3), also referred to as fetal liver kinase-2 (flk-2) or STK-I, is mainly expressed on the surface of hematopoietic stem and progenitor cells, in particular early myeloid and lympoid progenitor cells. It binds to Flt3L to form homodimers which activate signalling involved in proliferation, differentiation and apoptosis of hematopoietic stem and progenitor cells during normal hematopoiesis. Said dimerization results in activation of its tyrosine kinase domain, receptor autophosphorylation and subsequent recruitment of downstream signalling molecules such as the p85 subunit of PI3K (phosphatidylinositol 3 kinase), PLC-gamma (Phospholipase-C gamma), STAT5a (signal transducer and activator of transcription 5a), and SRC family tyrosine kinases (Gilliland and Griffin, Blood (2002) 100(5), 1532-42; Drexler, Leukemia (1996) 10(4), 588-99 and Ravandi et al., Clin Cancer Res. (2003) 9(2), 535-50). Activation of these downstream signalling molecules by phosphorylation leads to the proliferative and pro-survival effects of FLT3 (Gilliland and Griffin (2002) and Levis and Small, Leukemia (2003) 17(9), 1738-52).
In hematological malignancies, FLT3 is expressed at high levels or FLT3 mutations cause an uncontrolled induction of the FLT3 receptor and downstream molecular pathway. Hematological malignancies include leukemias, lymphomas (non-Hodgkin's lymphoma), Hodgkin's disease (also called Hodgkin's lymphoma), and myeloma- for instance, acute lymphocytic leukemia (ALL), acute myeloid leukemia (AML), acute promyelocytic leukemia (APL), chronic lymphocytic leukemia (CLL), chronic myeloid leukemia (CML), chronic neutrophilic leukemia (CNL), acute undifferentiated leukemia (AUL), anaplastic large-cell lymphoma (ALCL), prolymphocytic leukemia (PML), juvenile myelomonocyctic leukemia (JMML), adult T-cell ALL, AML with trilineage myelodysplasia (AML/TMDS), mixed lineage leukemia (MLL), myelodysplastic syndromes (MDSs), myeloproliferative disorders (MPD), multiple myeloma, (MM) and myeloid sarcoma (Kottaridis, P. D., R. E. Gale, et al. (2003). “Flt3 mutations and leukaemia.” Br J Haematol 122(4): 523-38). Myeloid sarcoma is also associated with FLT3 mutations (Ansari-Lari, Ali et al. FLT3 mutations in myeloid sarcoma. British Journal of Haematology. 2004 Sep. 126(6):785-91).
Mutations of FLT3 have been detected in about 30% of patients with acute myelogenous leukemia and a small number of patients with acute lymphomatic leukemia or myelodysplastic syndrome. Patients with FLT3 mutations tend to have a poor prognosis, with decreased remission times and disease free survival. There are two known types of activating mutations of FLT3. One is a duplication of 4-40 amino acids in the juxtamembrane region (ITD mutation) of the receptor (25-30% of patients) and the other is a point mutation in the kinase domain (5-7% of patients). These mutations most often involve small tandem duplications of amino acids within the juxtamembrane domain of the receptor and result in tyrosine kinase activity. Expression of a mutant FLT3 receptor in murine marrow cells results in a lethal myeloproliferative syndrome, and preliminary studies (Blood. 2002; 100: 1532-42) suggest that mutant FLT3 cooperates with other leukemia oncogenes to confer a more aggressive phenotype.
Specific inhibitors of FLT3 kinase therefore present an attractive strategy for the treatment of hematopoietic disorders and hematological malignancies. It was as such an object of the present invention to provide compounds and compositions comprising said compounds, acting as inhibitors of receptor tyrosine kinases, in particular as inhibitors of FLT3 (FMS-Related Tyrosine kinase 3).
We have now found that macrocyclic pyrazolopyrimidines can act as kinase inhibitors in particular FLT3 kinase inhibitors.
Several (non-macrocyclic) pyrazolopyrimidines have already been suggested as kinase inhibitors for the treatment of proliferative diseases such as cancer. For example:                WO2007044420: inhibition of CDK—treatment of cancer, . . .        WO2009097446: inhibition of PI3 Kinase—treatment of cancer        WO2010036380: inhibition of PI3 Kinase—treatment of cancer        WO2008037477: inhibition of PI3 Kinase—treatment of proliferative diseases, . . .        WO2006050946: inhibition of c-Abl, c-Src, . . .—treatment of proliferative diseases        WO2011003065: inhibition of JAK—treatment of cancer, leukemia, . . .        WO2010119284: inhibition of FGFR kinase—treatment of cancer        
However, none of the compounds disclosed in said references have been shown to have FLT3 inhibitory activity. Furthermore, the currently developed FLT3 kinase inhibitors, do not comprise macrocyclic pyrazolopyrimidine moieties (see for example WO2004039782, WO2007048088, WO2008016665, WO2009017795, WO2009109071). The compounds disclosed herein are therefore distinguishable from the prior art compounds in structure, pharmacological activity, potency and kinase selectivity.